non-linear regression

Growth traits (such as body weights at different ages) in most of the birds have been often considered in most of the poultry breeding programs. Changes in growth pattern can be evaluated through measuring body weight traits at regular intervals and using mathematical functions (growth curve functions). For this purpose, data from 1182 wild (including 905 female and 277 male) and 674 Italian speckled (including 499 female and 175 male) quails were utilized. Accordingly, after body weight at hatch, body weights of the birds were recorded through 45 days in a 5-day interval manner. Gompertz, Logistic, Lopez, Richards, and von Bertalanffy were used to estimate growth curve parameters. To evaluate/ rank the goodness of fit for functions, the BIC, AIC, MSE, and  were used. Based on results, Richards’ function for both studied populations (wild and Italian speckled quails) and for both genders (females and males) were the best fitted model. The relatively same growth pattern and same function for describing growth pattern in these two quail strains refer to the same growth traits, therefore simultaneous production of them can be achieved under same management practices. Moreover, comparing results of the current studies with other researches, by comparing other studies with this study’s results, it can be concluded that increasing the number of records and shortening the weighing intervals can be effective in determining the appropriate function.